The invention relates to a functional hydro-elastic element to be lodged in a hydro-elastic joint for damping load vibrations between two structural parts, in particular a wheel suspension and a vehicle body, the functional hydro-elastic element having a longitudinal axis and a circumferential direction around this longitudinal axis. Besides, the invention relates to a hydro-elastic joint for assembling two structural parts, in particular to connect a wheel suspension to a vehicle body, the joint comprising a longitudinal axis, a rigid external frame, a rigid internal frame, and a functional hydro-elastic element linking the internal frame to the external frame in a vibration-damping manner.
In particular, the invention relates to hydro-elastic joints for automobiles or heavy vehicles. In the present case, it more particularly concerns joints, in particular multi-layer joints, for ground connection of wheeled vehicles, wherein the joint has to provide an acoustic filter for structure-borne vibrations. Typically, these joints must have a significant radial stiffness in view of the occurring stresses and of the joints' guiding function; thus, these high stiffnesses facilitate the transmission of noise.
Hydro-elastic mountings or joints are known for many years. These consist generally of at least two cylindrical, concentric frames, the annular space between which is filled with elastomer material in which hydraulic chambers are arranged and linked by channels. The liquid contained in these chambers can circulate from one chamber into the other for low excitation frequencies whereas from a certain frequency onwards an occurring resonance blocks passing of the liquid, which causes a phase shift associated with a dynamic stiffening used for filtering certain vibrations. This technique is explained in various patents such as U.S. Pat. No. 6,273,406.
There are numerous variants of shapes for hydro-elastic joints that can be classified into two families.
The first family comprises hydro-elastic joints having two hydraulic chambers opposite to each other at 180° according to a preferential radial direction corresponding to the principal excitation direction, or four hydraulic chambers opposing each other pairwise according to two radial directions that are orthogonal to each other. This is for example the case for the patent applications EP 1 348 885 and FR 2817007.
The second family comprises hydro-elastic joints designed with a peripheral hydraulic chamber that is continuous but that can locally present throttling areas in the hydraulic circuit. This is for example particularly the case for the patent application FR 2 910 577 and the application EP 0410455.
The variations in these two families originate either from the two connection principles, one or double layer, or from the way the hydraulic chambers and channels are built, that is with or without an incorporated plastic piece. Finally, there are joints for filtering radial excitations and others for filtering axial excitations with hydraulic effect, wherein the axis is the axis of the cylindrical frames of the joint. Some rare applications provide the ability of filtering with hydraulic effect at the same time in axial and in radial direction. This is the case for the patent application FR 2 659 713 and in certain embodiments of the application FR 2 910 577.
The patent application FR'713 claims to provide hydraulic filtering in all radial directions with four hydraulic chambers. However, the breakdown of stresses it describes does not compensate for the fact that a hydraulic chamber exposed to a load that essentially differs from a radial direction will not be able to eject the hydraulic liquid in the same way as if the load was purely radial, that is perpendicular to the external surface of the hydraulic chamber. Additionally, despite the fact that the four peripheral chambers of the joint disclosed in FR'713 provide filtering in all directions, the level of filtering will not be constant depending on the radial direction, which prohibits mounting such a joint without specific angular orientation.
The patent application FR'577 discloses a continuous and peripheral hydraulic chamber that a priori seems ideal to assure homogenous hydraulic filtering in all radial directions. However, the fluid transfer from an area subjected to an excitation towards a diametrically opposed area is only really controllable if a debit restriction is present at a specific location, as it is also disclosed in the application FR'577. Thus, if during mounting the joint is angularly oriented such that this restricted area is directly above the radial axis of excitation, the flow of liquid will be strongly inhibited and the fluid will have a tendency to be repelled towards the two half-chambers at each side of the restricted area. This generates the risk of creating a phase shift already for low frequencies through blockage of the hydraulic fluid. In order to avoid localised peripheral restrictions, a solution with a hydraulic chamber in the shape of a very thin layer could be considered, as in the application FR'577, but this arrangement is industrially problematic in view of the inevitable tolerances of manufacturing.
Thus, the prior concepts of hydro-elastic joints require a specific orientation for the assembly, that is either angularly because they do not hydraulically filter in an essentially constant manner over all radial directions, or axially because they cannot be mounted head to head, or in both directions because they can only filter either radially or axially.
Furthermore, the frequencies or frequency ranges to be absorbed for a hybrid or electric vehicle are different from the frequency ranges for a vehicle solely driven by a combustion engine. Hybrid vehicles can be driven in parallel or sequentially by an electric motor and a combustion engine. For example, if the hybrid vehicle is driven solely by an electric motor, a driver can hear noises that are normally masked by the noise or the vibration of the combustion engine. For example the noise of a gearbox or of a transmission can be disturbing for a passenger.